An optical parametric amplifier (OPA), as an important optical device in the technical field of lasers, is widely used in fields such as scientific research, medicine and industrial engineering etc. The work principle of OPA is to emit a high-frequency laser beam ωp and a low-frequency laser beam ωs into a nonlinear medium simultaneously. Energy of the high-frequency laser beam ωp is transferred onto the low-frequency laser beam ωs due to a difference frequency effect therebetween, so that the low-frequency laser is amplified, and a third laser beam termed as idler wave with a frequency ωi is obtained, wherein ωp>ωs, and ωp=ωs+ωi, wherein ωp is generally termed as pump wave, and ωs is generally termed as signal wave.
However, all parametric processes will be subject to backconversion, which means that the energy will reflow from the signal wave and the idler wave towards the pump wave when the pump wave decays strongly and the parametric processes go into saturated amplification. Therefore, such an energy reflow effect greatly limits the ultimate performance of the optical parametric amplifier.